Abstract The effective block approach is a concept where the crack growth rates are quantified and modelled by treating a block of variable amplitude (VA) loading as being similar to a single cycle of constant amplitude (CA) loading, but with a greater amount of energy compared to a single CA cycle. The fatigue crack growth rate (FCGR) per block can be determined for a certain VA spectrum and for lead cracks the crack growth rate shows a linear relationship with the crack length (exponential crack growth) and a cubed relationship with the reference stress (i.e. maximum spectrum stress) (Molent and Jones 2016). The applicability of the cubic rule for standardized test specimens is investigated by varying the reference stress between middle tension specimens. A short VA sequence from a combat wing root bending moment spectrum is applied to the specimens and is constantly repeated during the test. The crack length versus cycles curve is fitted directly to obtain accurate crack growth rates by assuming power law behaviour at all crack lengths and the presence of pivot points where the slope in crack growth rate is able to change at specific crack lengths. The resulting changes in VA long crack growth rates are correlated to the changes in crack length for a given reference stress and to the changes in reference stress between specimens. Translation of the VA FCGRs in the exponential crack growth regime for different reference stresses indicates that the exponent of the reference stress is 2.12. This is in contrast with an exponent of two on the reference stress if VA loading is governed by the reference stress intensity factor only or an exponent of three if the lead crack approach is applicable.


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    Title :

    Effect of Crack Length and Reference Stress on Variable Amplitude Fatigue Crack Growth Rate


    Contributors:


    Publication date :

    2019-07-03


    Size :

    12 pages





    Type of media :

    Article/Chapter (Book)


    Type of material :

    Electronic Resource


    Language :

    English